1. Field of the Invention
This invention relates to the field of optimization of spatial databases for functional purposes, and in particular to optimize spatial data to achieve minimal download data size for use with cartographic applications in a networked environment.
2. Discussion of Prior Art
A spatial database comprises topographic information in the form of shapes, lines and points encoded with geodetic coordinates, as well as sets of attributes further describing each form. Internet-based applications use the spatial database to generate bitmap images based on user input such as zip code or address on a server and transmit the map images to client devices. Bitmap-based solutions have numerous limitations, which are well known in the art. While prior art describe systems, which transfer vector data to client devices instead of bitmaps, bitmap solutions remain more efficient in terms of data transfer overhead. The initial download size of vector data is significant, and unless the user interacts repeatedly with the map, the total data amount of vector data is greater than the total data amount of bitmap images. Even if the user interacts frequently with the map and the total download size requirements for bitmap and vector data were about the same, most users prefer to have a number of shorter download wait times rather than one long download wait time. Therefore, except for a few non-mainstream applications, bitmap-based solutions are widely used in networked applications.
In navigation systems, a navigation application and spatial data are packaged and supplied as a complete system on a non-volatile storage medium. Said navigation systems may be installed in vehicles or in standalone devices. These navigation systems rely on significant computing resources such as powerful processors and large permanent storage capacities. Prior art introduces solutions, which use structuring and segmenting of spatial databases to improve data access times and navigational functionality. Said solutions are not applicable when computing resources are severely limited, as encountered on personal digital assistants and smartphones, on which one would want to have access to navigation capabilities and maps. Even when said resources are made available for car navigation systems, more powerful hardware results in higher cost for the system. More importantly still, since spatial data changes quite frequently, standalone car navigation systems will inevitably start producing out-of-date navigation instructions over time. It is therefore necessary to update the local database from time to time. Improved methods for updating said local databases have been introduced by prior art. Nevertheless, the requirement to repeatedly update data used by navigation systems remains a major inconvenience for both consumers as well as navigation system suppliers. Suppliers face substantial costs for creating and distributing the data in regular intervals, and any errors discovered after storing data sets on non-volatile media are costly to fix. To address the above problems, it is desirable to keep frequently changing spatial data on a central server and use wireless transmission networks to deliver navigation functionality to remote devices. Navigational functions such as route calculation and driving directions are performed on the server, making it also easier to integrate real-time road traffic condition data. Driving directions or maneuver instructions are text-based and relatively small in terms of data size, allowing for fairly quick wireless data transmission. On the other hand, the ability to provide graphical, cartographic map display introduces much larger data size overhead. Given the data transfer rates of wireless networks presently and during several years to come, users would experience unacceptably slow performance for map display functionality on remote devices.
The objective of this invention is to introduce a new spatial database system, which reduces the data size, makes it possible to download data in small increments as needed, and which can be used with applications such as navigation systems, for which vector-based functionality is needed.
The primary object of the invention is to provide a compressed spatial database system, which enables incremental and efficient download of spatial vector data over a network. Another object of the invention is to introduce a location-relevant naming system so that software running on network client devices can efficiently compute data segment file names depending on user interaction with a map or device-supplied location data (e.g. GPS). A third object of the invention is to enable combined online and offline operation capability of a digital map display system. Another object of the invention is to provide server-independent map display capability based on GPS location input. A further object of the invention is to introduce a system allowing updating of dynamic location content without having to retransmit redundant map data. Yet another object of the invention is to enable map centering despite using a segmented data system.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
In a preferred embodiment of the present invention, a method for organizing and compressing spatial data comprises the steps of parsing a spatial database, separating topographic from attribute information, segmenting the data into rectangles, eliminating subsets of the data points, further reducing the data size by converting the data from a real number format to an integer format, generating location-relevant file names for each of the rectangles and storing the files in permanent storage space. In accordance with a preferred embodiment of the present invention, map display client software computes data file names based on user interactions or device-supplied location information (GPS), fetches the computed file names from a remote server, combines data from several data files to produce an in-memory map image and draws the image on the display screen.